High speed ground transportation system

ABSTRACT

A HIGH-SPEED GROUND TRANSPORATATION SYSTEM COMPRISES A DUCT THROUGH WHICH A VEHICLE IS ADAPTED FOR PROPULSION AS A FREE PISTION. ENTRANCE AND EXIT VALVES ARE PROVIDED ADJACENT THE ENDS OF THE DUCT AND THE SECTION OF THE DUCT BETWEEN THE VALVES IS PREVACUATED. ON OPENING THE ENTRANCE VALVE, AIR PRESSURE FORCES THE VEHICLE INTO THE SECTION AND AFTER THE VEHICLE HAS PASSED THE ENTRANCE VALVE AND A PREDETERMINED AMOUNT OF PROPULSIVE AIR HAS AN ENTERED THE DUCT BEHIND THE VEHICLE, THE VALVE IS CLOSED. A CUT-OFF VALVE IS PROVIDED IN THE DUCT DOWNSTREAM THE ENTRANE VALVE FOR PREVENTING THE PROPULSION AIR ADMITTED BEHIND THE VEHICLE FROM ENTERING THE MAIN BODY OF THE DUCT. THE EXIT VALVE OPENS WHEN THE PRESSURE AHEAD OF THE VEHICLE REACHES A PREDETERMINED PRESSURE.

Sept. 20, 1971 L. K. EDWARDS HIGH SPEED GROUND TRANSPORTATION SYSTEM 3Sheets-Sheet 1 Filed Sept. 5, 1969 P 20, 1971 L. K. EDWARDS 3,605,629

HIGH SPEED GROUND TRANSPORTATION SYSTEM Filed sept. 5, 1969 sSheets-Sheet 2 525 75 M i 2? M .74. 1!] II If Q i if L 1H IH HI 1 3 5,4M I w 5/2 3/; Fl 6 4A 525 7 355 A //5 A A35 fit l 5/5 *d qi|:% $1" J HIHI 1 1 a. W FIG. 4c

MR 5.. z A111 w 6M 56 3 g /A F 4 F 7A United States Patent O:

3,605,629 Patented Sept. 20, 1971 hoe 3,605,629 HIGH SPEED GROUNDTRANSPORTATION SYSTEM Lawrence K. Edwards, 301 Santa Rita Ave., PaloAlto, Calif. 94301 Filed Sept. 3, 1969, Ser. No. 854,887

Int. Cl. B61b 13/10; B65g 51/04 U.S. Cl. 104-438 21 Claims ABSTRACT OFTHE DISCLOSURE A high-speed ground transportation system comprises aduct through which a vehicle is adapted for propulsion as a free piston.Entrance and exit valves are provided adjacent the ends of the duct andthe section of the duct between the valves is preevacuated. On openingthe entrance valve, air pressure forces the vehicle into the section andafter the vehicle has passed the entrance valve and a predeterminedamount of propulsive air has entered the duct behind the vehicle, thevalve is closed. A cut-off valve is provided in the duct downstream fromthe entrance valve for preventing the propulsive air admitted behind thevehicle from entering the main body of the duct. The exit valve openswhen the pressure ahead of the vehicle reaches a predetermined pressure.

BACKGROUND OF THE INVENTION The invention is particularly concerned withimprovements in high-speed ground transportation systems of the type inwhich a vehicle is propelled as a free piston through a tube or duct bydifferential air pressure between the front and rear of the vehicle,such as are disclosed in copending United States patent application Ser.No. 720,408, filed Apr. 10, 1968 and United States Pat. No. 3,404,638,each entitled High-Speed Ground Transportation System.

In said United States patent application Ser. No. 720,- 408, there isshown a high-speed ground transportation system comprising a duct, avehicle adapted for propulsion as a free piston through the duct bydifferential air pressure on the rearward and forward ends of thevehicle, a valve for the duct adjacent one end of the duct and a valvefor the duct adjacent the other end of the duct, these valves beingadapted when closed to block off a section of the duct from valve tovalve. This section is evacuated prior to entry of a vehicle therein.The duct has end portions outward of the valves constituting air locksor stations which are open to the atmosphere. In operation, startingwith the vehicle in a first station, the corresponding valve (serving asan entrance valve) is opened for propulsion of the vehicle therethroughpropelled by atmospheric pressure acting on the rear of the vehicle. Theentrance valve is closed after the rearward end of the vehicle haspassed thereby, so as to trap a slug of atmospheric air in the duct.This slug of air expands to continue topropel the vehicle through theduct until the pressure of air rearward and ahead of the vehicle isequalized. The vehicle then coasts forward under the kinetic energybuilt up therein, compressing air ahead of the vehicle, and opening theother valve (serving as an exit valve) when the pressure of air ahead ofthe vehicle generally equals atmospheric pressure for exit of thevehicle from said section, the vehicle passing into and being stopped inthe second station and the exit valve closing behind the vehicle. Thereis also shown a system in which a second duct extends parallel to thefirst duct for travel of vehicles in opposite directions on the sameroute. The two ducts are provided with cross-connections or cross-ductsfor circulation of air around the vehicle as it traverses one of theducts, and with auxiliary valves (indicated at 25 in said applicationSer. No. 720,408). This system is used for long stages, ten miles orlonger, for example. Recent analysis indicates that the combinedpneumatics and gravity can accelerate the vehicle rapidly to high speed.As the vehicle reaches a high speed, e.g., of the order of four hundredmiles per hour, the flow losses in the air column behind the vehiclebecome so large that the pressure immediately behind the vehicle dropsto near vacuum even though the entrance valve and auxiliary valves arestill open. Thus the air behind the vehicle is no longer capable ofimparting energy to the vehicle and it would be fruitless to admit moreair or to expand the air already in the duct. To this end, the entrancevalve and auxiliary valves are closed. In addition, the open cross-ductsserve to equalize pressure around the train or vehicle. Recent analysisindicates that there may be a rise of the order of 2 p.s.i. in theambient duct pressure if the several-mile-long accelerating air slug ispermitted to expand and diffuse via the cross-ducts throughout the pairof ducts. A second vehicle, being propelled through the opposite duct atthe same time would cause still higher pressure rise and consequenthigher losses.

SUMMARY OF THE INVENTION Among the several objects of this invention maybe noted the provision of an improved high-speed ground transportationsystem of the class above described and method of operation thereof inwhich the propulsive air admitted behind the vehicle is prevented fromexpanding throughout theduct, thereby permitting lower pressures to bemaintained during the coast phase of the trip with the result of lowerlosses and higher overall efiiciency of the system; the provision ofsuch a system in which relatively low-power pumping equipment may beused; and the provision of an improved system as above described andmethod of operation thereof which reduce to a minimum the effect of avehicle traveling in one direction in one of the ducts on a vehicletraveling in the other direction in the other duct.

In general, a high-speed ground transportation system of this inventioncomprises a duct adapted for propulsion of a vehicle therethrough as afree piston by differential air pressure on the ends of the vehicle.Entrance and exit valves are provided for the duct. The entrance valveis adapted to close a suitable time after the rearward end of thevehicle has passed and a predetermined amount of propulsive air hasentered behind the vehicle in the duct, thus controlling the energyinput to the vehicle. A cut-01f valve is provided for the ductdownstream from the entrance valve adapted to close after the rearwardend of the vehicle has passed thereby to trap the propulsive air betweenit and the entrance valve, thereby preventing the accelerating air slugfrom expanding throughout the duct. This decreases the duct pressure forthe coast phase of the trip. If the duct is interconnected with anotherduct for passage of a vehicle in the opposite direction, this alsoavoids an undesirable rise in forces resisting free passage of a vehiclethrough the opposite duct. In the operation of the system, starting withthe vehicle in the duct outward of the entrance valve, the entrance andexit valves closed, the section of the duct between these valvesevacuated, and the cut-off valve open, the entrance valve is opened forentrance of the vehicle into the duct and propulsion of the vehicletherethrough. The entrance valve is closed after the rearward end of thevehicle has passed and a predetermined amount of propulsive air hasentered the duct behind the vehicle, and the cut-01f valve is closedafter the rearward end of the vehicle has passed thereby to trap thepropulsive air between the cut-off valve and the entrance valve. Otherobjects and features will be in part apparent and in part pointed outhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view insection of a highspeed ground transportation system of this invention;

FIG. 2 is a section showing a cut-01f valve of this invention;

FIG. 3 is a section on line 3--3 of FIG. 2; and

FIGS. 4A-4L are views illustrating a trip of a vehicle in a double-ductsystem of this invention.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawings, there is indicated at 1 a subterranean tube or duct extendingfrom a station S1 to a station S2 along the route of a transportationsystem and continuing on from station S2. At 3 is indicated a vehicleadapted for propulsion as a free piston through the duct by differentialpressure of air between the rear and the front of the vehicle. Entranceof the vehicle from station S1 to the duct is via an entrance valve 5 atthe entrance end of the duct. Exit of the vehicle from the duct tostation S2 is via an exit valve 7 at the exit end of the duct. Thevalves 5 and 7 may be of the type shown in application Ser. No. 710,582,filed Mar. 5, 1968, by Lawrence K. Edwards and Bruce E. Skov, entitledHigh- Speed Ground Transportation System.

Valves 5 and 7, when closedfblock 01f a section B of the duct from valveto valve between stations S1 and S2. Provision is made for evacuatingthis section of the duct down to low pressure (of the order of onep.s.i., or even one-fifthp.s.i., for example), as by means of anevacuating pump 40. Each station is adapted for entry of atmospheric air(for pressurizing the rear of a departing vehicle or discharge of airahead of an arriving vehicle) via a shaft 9.

It is feasible to utilize an additional propulsive power source, namely,gravity, by sloping the duct downward from the stations as shown inFIG. 1. That is, the duct descends to a greater depth bet-ween stationsthan at the stations in an arc of predetermined contour or profile. Itmay descend to a depth of up to 3,500 feet, for example. With thisarrangement, gravity is utilized to increase the acceleration of thevehicle leaving station S1 and to increase the deceleration of thevehicle approaching station S2, interchanging potential and kineticenergy with the same high efficiency as a pendulum. Thus, as the vehicletraverses the downward slope of the are it is accelerated both bygravity and by the differential air pressure on its front and rear.Similarly, as the vehicle traverses the upward slope of the arc it isdecelerated by gravity and compression of air ahead of it, with the lossin speed due to gravity being equal to the gain in speed attained fromgravity in the down slope.

In accordance with this invention, a cut-01f valve 1.3 is provided inthe duct downstream from the entrance valve 5. The cut-ofi valve 13 isadapted to close after the rearward end of the vehicle has passedthereby to trap the propulsive air between it and the entrance valve toprevent this slug of air from expanding throughout the duct, therebyavoiding an increase in the pressure in the duct for the coast phase ofthe trip between stations S1 and S2. This increases the overallefliciency of the system, particularly in a double-duct system, as willappear. As shown in FIGS. 2 and 3, the cut-off valve 13 may comprise agate 15 slidable in a housing 17 for movement between an open orretracted position out of the duct and a closed position extendingacross the duct (shown in phantom in FIGS. 1 and 3). The piston rod of adoubleacting pneumatic actuator or air cylinder 19 is secured to thegate for moving it into and out of the duct in response to operation ofa control valve 21. Pneumatic energy for actuating the cylinder 19 isreadily drawn from the near vacuum normally existing in the adjacentduct, as indicated at 23, and through a port 24 open to atmosphere. Areservoir 25 is provided to store energy for periods when conditionsother than vacuum exist in the duct, and a safety latch 27 locks thegate 15 in its retracted position. A check valve 28 is provided betweenthe duct and the reservoir. Control valve 21 is adapted to be set in afirst position for drawing a vacuum in the upper end of cylinder 19 andsupplying air under atmospheric pressure to the lower end of thecylinder 19 for retracting the gate, and in a second position fordrawing a vacuum in the lower end of cylinder 19 and supplying air underatmospheric pressure to the upper end of the cylinder 19 for closing thegate.

FIGS. 4A-4L illustrate a double-duct system of this invention whichcomprises a pair of ducts, designated 1A and 1B, located side-by-sidefor travel of vehicles in opposite directions on the same route. The twoducts are cross-connected at suitably spaced intervals along theirlength by cross-ducts 29, each of which may have a control valve thereinas indicated at 31. The valves 31 are not always necessary for thepractice of the instant invention and the system may preferably beoperated without them or with them open at all times. There are airlocks or stations 81A and 82A at the ends of duct 1A and stations SIBand 82B at the ends of the duct 1B (corresponding to stations S1 and S2of duct 1 of FIG. 1). There are entrance and exit valves 5A and 7Aadjacent the ends of duct 1A and entrance and exit valves 5B and 7Badjacent the ends of duct 13 (corresponding to the valves 5 and 7adjacent the ends of the duct 1 of FIG. 1). Each duct 1A and 1B may alsohave a series of auxiliary valves designated 33A and 33B spaced atintervals along the length of the duct immediately inward of eachentrance and exit valve at both ends of the duct. Each of these valves33 is in communication with the ambient atmosphere and is adapted, whenopened, to admit atmospheric air to the respective end of the section Bof the respective duct. These valves are not always necessary and thesystem may preferably be operated according to the instant inventionwithout them or with them closed at all times. Additionally, each duct1A and 13 has a cut-off valve 13A and 13B between the last auxiliaryvalve 33, if provided, and in any event between the entrance valve 5 atthe entrance end of the duct and the first cross-duct 29. The valves 13Aand 13B, when closed, form a pressure barrier between the portions ofthe duct to either side of the valve and, when open, permit passage of avehicle.

The mode of operation of the FIG. 4A double-duct system for travel ofvehicle 3 through duct 1A from station 51A to 52A will now be described,and it will be apparent from this how the system is operated for travelof a vehicle in the opposite direction through duct 1B. As shown in FIG.4A, the vehicle 3 is at rest in station SlA at the left end of duct 1A.Initially, main valves 5A, 7A, 5B and 7B are closed. Auxiliary valves33A and 33B, if provided, are closed and cut-ofl? valves 13A and 13B andcross-duct valves 31, if provided, are open. Section B of each of ducts1A and 1B has been evacuated down to low pressure (of the order of onep.s.i., or even one-fifth psi, for example). The trip of the vehiclethrough duct 1A is initiated by opening valve 5A.

As a result of opening valve 5A, and with nearvacuum ahead andatmospheric pressure behind, the vehicle 3 is propelled through station81A and into section B of the duct, as indicated in FIG. 4B. As thevehicle progresses further into the duct, the entrance valve 5A remainsopen and, if desired, although usually not necessary, the auxiliaryvalves 33A at the left end of the duct are opened in succession as therearward end of the vehicle passes thereby, thus admitting additionalat:

mospheric air into the duct behind the vehicle. Although the pressure onthe rear of the vehicle drops somewhat due to flow losses in the tube,the vehicle continues to accelerate due to greater pressure behind thanahead and the downward slope of the duct as shown in FIG. 4C.

When a predetermined amount of pneumatic energy has been imparted to thevehicle, the entrance valve 5A and the auxiliary valves 33A at the leftend of the duct (if any had been opened) are closed, as shown in FIG.4D, trapping a slug of accelerating air between the valve SA and therear end of the vehicle. This slug of air in the duct behind the vehicleexpands causing the pressure to drop and propelling the vehicle forward,with the vehicle continuing to accelerate, though at a diminishing rate,as the slug of air expands. The pressure immediately behind the vehicledrops faster than the average pressure in the duct behind the vehiclebecause of airflow losses in the duct.

As the vehicle passes through the cut-off valve 13A, it is nearingcruise speed. Soon after the vehicle has passed, the valve 13A is closedtrapping the accelerating air slug between it and the entrance valve 5A.The small amount of air trapped between the valve 13A and the vehiclerapidly expands to a low pressure. After the vehicle passes the firstcross-duct the vehicle coasts circulating the thin air as indicated inFIG. 4F. If, as the vehicle passes each cross-duct, the air between therear of the vehicle and valve 13A has not expanded down to the ambientpressure existing in tube 1B, and if valves are provided in thecross-duct, the cross-duct valve 31 may be closed as the vehicle passesas shown in FIG. 4B and then reopened once the pressure behind thevehicle equalizes with that in tube 1B. The thin air will then circulateas indicated above and as shown in FIG. 4F.

The vehicle continues to coast with some loss of speed through duct 1A,air ahead of the vehicle passing from duct 1A via the cross-connections29 ahead of the vehicle (the valves 31 of which, if provided, are open)to duct 1B and thence via duct 1B and the cross-connections 29 rearwardof the vehicle (the valves 31 of which, if provided, are open) back toduct 1A behind the vehicle, as shown in FIG. 4G. At a predetermined time(dependent on vehicle weight, velocity and other system parameters), theremaining cross-duet valves 31, if any, ahead of the vehicle are closed,as shown in FIG. 4H, and the vehicle begins to compress the thin airahead, thereby increasing the pressure of air ahead and retarding thevehicle. As each cross-duct valve 31, if any, is passed, it is againopened. In any event, as it passes the last cross-duct it will compressthe thin air ahead with the results as indicated supra.

The vehicle continues to decelerate at an increasing rate as it climbsthe slope to station 82A and compresses the air ahead. The compressionof the air ahead of the vehicle continues as the vehicle travels forwarduntil the pressure of the air reaches essentially atmospheric pressure.At this point the exit valve 7A and auxiliary valves 33A, if any, at theright end of the duct are opened, as shown in FIG. 41, and the air aheadof the vehicle is forced out of the duct while remaining at nearatmospheric pressure. Normally, auxiliary valve(s) 33A will not beneeded, but it can be used to provide an additional escape path for theair and thereby reduce losses and associated pressure rise on the frontof the vehicle. With near-vacuum behind and atmospheric pressure ahead,the vehicle decelerates rapidly. The auxiliary valve 33A, if provided,is closed when the vehicle passes thereby, as indicated. in FIG. 4]. Thevehicle continues to decelerate and comes to a stop in station SZA andthe exit valve 7A is closed behind the vehicle as shown in FIG. 4K.

Vacuum pumps 40 are connected to each duct. These pumps may beconfigured to operate more or less continuously, exhausting air from theducts. When the cut-01f valve 13A is closed, the pump exhausts air fromthe region between the valve 13A and the entrance valve 5A thus removingthe accelerating air slug after the vehicle passes. Once the air slug isremoved and the pressure across the cut-01f valve is equalized, thecut-off valve is opened and the system is ready for another trip, asshown in FIG. 4L.

Propulsion of a vehicle in the opposite direction through duct 1B iseffected in a similar manner. It will be observed that, as regardstravel of the vehicle through duct 1A, duct 1B serves as an auxiliaryduct, in conjunction with the cross-connections 29, for passage of airfrom ahead of the vehicle to behind the vehicle during the intermediatecoasting phase of the trip. The addition of valves 33 may beadvantageous for more rapidly and efiiciently admitting air to the ductbehind the vehicle at the start of a trip for accelerating the vehicleand for more rapidly and efficiently pushing air out of the duct aheadof the vehicle at the conclusion of a trip when the pressure in the ductahead of the vehicle has reached atmospheric pressure. However, the useof such valves is not always necessary for the practice of the instantinvention. Valves may also be placed in the cross-ducts so that a singletube can be repressurized in an emergency.

Neglecting losses due to air circulation, heat transfer, drag androlling friction, the momentum of the vehicle is sufiicient to eject thesame amount of air in the last phase of the operation as was taken induring the initial phase of the operation, and each succeeding trip ofthe vehicle, apart from these losses, is a relatively free trip, i.e.,it requires no additional power except that which may be needed to makeup for said losses.

From the above, it will appear that the cut-off valve 13A (as to duct1A) and the cut-off valve 1313 (as to duct 1B) advantageously capturesthe accelerating air slug so that the latter is not allowed to dispersethroughout the double-duct system. Thus, a lower pressure can bemaintained for the coast phase of the trip with the result of lowerlosses. It should be noted that it may be necessary to allow a portionof the accelerating air slug to disperse throughout the system, so thatthere is sufiicient air in the ducts for the compression phase as thevehicle approaches the end of a trip. Careful sizing of the pump mayavoid this problem.

The fact that the accelerating air slug is not allowed to dispersethroughout the double-duct system reduces to a minimum the effect ofvehicles traveling in opposite directions in the ducts. Since 'a singlevehicle (in one duct) does not appreciably alter the ambient conditionsin the cross-vented section of the double-duct system, a vehicle in theother duct will not be aifected by the presence of the first vehicleexcept for a small change in air circulation losses as the vehiclespass. Thus, operation of the vehicle in one tube is essentiallyindependent of the presence of a vehicle in the other tube.

It will be understood that the principles of the doubleduct system withthe valved cross-connections and the entrance and exit valves at theends of the ducts may be utilized in a single-duct system, as to whichthe place of the second vehicle duct would be taken by a second orauxiliary duct cross-connected to a single vehicle duct.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and. not in alimiting sense.

What is claimed is:

1. A high-speed ground transportation system comprising a duct adaptedfor propulsion of a vehicle therethrough as a free piston bydifferential air pressure on the ends of the vehicle, said duct havingan entrance end and an exit end each in communication with the earthsatmosphere, an entrance valve for the duct downstream from and adjacentits entrance end, an exit valve for the duct adjacent its exit end, theentrance valve being adapted to close after the rearward end of thevehicle has passed and a predetermined amount of propulsive air hasentered behind the vehicle in the duct, a cut-oft valve for the ductdownstream from the entrance valve adapted to close after the rearwardend of the vehicle has passed thereby to trap the propulsive air betweenthe cut-01f valve and the entrance valve, and an auxiliary valve inwardof the entrance valve for admission of additional propulsive air, saidauxiliary valve being located between the entrance valve and the cut-offvalve.

2. A high-speed ground transportation system as set forth in claim 1having a series of auxiliary valves inward of the entrance valve foradmission of additional propulsive air, said auxiliary valves beinglocated between the entrance valve and the cut-ofi? valve.

3. A high-speed ground transportation system as set forth in claim 1wherein said cut-01f valve comprises a gate movable between a retractedposition clear of the duct and a closed position blocking the duct.

' 4. A high-speed ground transportation system as set forth in claim 2and including a pneumatic actuator for the gate, and a control valve forthe actuator interconnected with the duct and having a port incommunication with the atmosphere.

5. A high-speed ground transportation system as set forth in claim 4further having a vacuum reservoir in the interconnection bet-ween thecontrol valve and the duct.

6. A high-speed ground transportation system as set forth in claim 1having a second duct paralleling said first-mentioned duct, andcross-ducts between said ducts.

7. The system of claim 6 wherein each cross-duct has a control valvetherein.

8. A high-speed ground transportation system as set forth in claim 6wherein the second duct is a vehicle duct having an entrance valve andan exit valve and adapted for propulsion of a vehicle therethrough as afree piston by difierential air pressure on the ends of the vehicle, theentrance valve for the second duct being adapted to close after therearward end of the vehicle in the second duct has passed and apredetermined amount of propulsive air has entered behind the vehicle inthe second duct, and a cut-off valve for the second duct downstream fromthe entrance valve for the second duct adapted to close after therearward end of the vehicle has passed thereby to trap the propulsiveair in the second duct between the cut-01f valve and the entrance valveof the second duct.

9. A high-speed ground transportation system as set forth in claim 8wherein the cut-otf valve for each duct is located between the entrancevalve and the first crossduct for the respective duct.

10. A high-speed ground transportation system as set forth in claim 9wherein each duct has an auxiliary valve inward of its entrance valvefor admission of additional propulsive air, each cut-off valve beinglocated between the auxiliary valve and the first cross-duct for therespective duct.

11. A high-speed ground transportation system as set forth in claim 9wherein each duct has a series of auxiliary valves in ward of itsentrance valve for admission of additional propulsive air, each cut-01fvalve being located between the innermost auxiliary valve and the firstcrossduct for the respective duct.

12. A high-speed ground transportation system as set forth in claim 8wherein each cut-oif valve comprises a gate movable between a retractedposition clear of the respective duct and a closed position blocking therespective duct, a pneumatic actuator for the gate, and a control valvefor the actuator interconnected with the respective duct and having aport in communication with the atmosphere.

13. A high-speed ground transportation system as set forth in claim 12further having a vacuum reservoir in 14. The method of operating ahigh-speed ground transportation system in which a vehicle is propelledas a free piston through a duct, the duct having an entrance valve andan exit valve adjacent its ends adapted when closed to block off asection of the duct from valve to valve, and a cut-otf valve downstreamfrom the entrance valve, comprising starting with the vehicle in theduct outward of the entrance valve, the entrance and exit valves closed,the cut-01f valve open, and said section of the duct between theentrance and exit valves evacuated, opening the entrance valve forentrance of the vehicle into the duct and propulsion of the vehicletherethrough, closing the entrance valve after the rearward end of thevehicle has passed and a predetermined amount of propulsive air hasentered the duct behind the vehicle, closing the cut-off valve after therearward end of the vehicle has passed thereby to trap the propulsiveair between the cut-off valve and the entrance valve, and opening theexit valve as the vehicle approaches the latter, the vehicle passinginto and being stopped in the other end of the duct and the exit valveclosing behind the vehicle.

15. The method of claim 14 wherein the duct has an auxiliary valveinward of the entrance valve communicating with the atmosphere, thecut-oif valve being located inward of the auxiliary valve, and wherein,at the start, the auxiliary valve is closed and is opened as the vehiclepasses thereby, the entrance valve and the auxiliary valve being closedafer a predetermined amount of air has been admitted behind the vehicle.

16. The method of claim 14 wherein the duct has a series of auxiliaryvalves inward of the entrance valve communicating with the atmosphere,the cut-otf valve being located inward of the innermost auxiliary valve,and wherein, at the start, the auxiliary valves are closed and aresuccessively opened as the vehicle passes thereby, the entrance valveand the auxiliary valves being closed after a predetermined amount ofair has been admitted behind the vehicle.

17. The method of operating a high-speed ground transportation system inwhich a vehicle is propelled as a free piston through a first duct, saidfirst duct having an entrance valve and an exit valve adjacent its endsadapted when closed to block off a section of the first duct from valveto valve, and a cut-off valve downstream from the first valve, therebeing a second duct alongside the first duct and crossducts between theducts spaced at intervals therealong, the cut-01f valve in the firstduct being located between the entrance valve for the first duct and thefirst cross-duct, comprising starting With the vehicle in the first ductoutward of the entrance valve for the first duct closed, the cut-0Evalve for the first duct open, and the ducts evacuated, opening theentrance valve for the first duct for entrance of the vehicle into thefirst duct and propulsion of the vehicle therethrough, closing theentrance valve for the first duct after the rearward end of the vehiclehas passed and a predetermined amount of propulsive air has entered thefirst duct behind the vehicle, closing the cut-off valve for the firstduct after the rearward end of the vehicle has passed thereby to trapthe propulsive air between the cut-off valve and the entrance valve forthe first duct, and opening the exit valve for the first duct as. thevehicle approaches the latter, the vehicle passing into and beingstopped in the other end of the first duct and the exit valve closingbehind the vehicle.

18. The method of claim 1'! wherein each cross-duct has a control valvetherein and as the vehicle passes through the duct the control valves inthe cross-ducts are closed as the vehicle passes and is subsequentlyreopened.

19. The method of claim 18 wherein the control valve in the firstcross-duct is closed as the vehicle passes thereby, and is subsequentlyreopened.

20. The method of claim 17 wherein the first duct has an auxiliary valveinward of its entrance valve communieating with the atmosphere, thecut-01f valve being located inward of the auxiliary valve, and wherein,at the start, the auxiliary valve is closed and is opened as the vehiclepasses thereby, the entrance valve and the auxiliary valve being closedafter a predetermined amount of air has been admitted behind thevehicle.

21. The method of claim 17 wherein the first duct has a series ofauxiliary valves in ward of its entrance valve communicating with theatmosphere, the cut-off valve being located inward of the innermostauxiliary valve, and

10 wherein, at the start, the auxiliary valves are closed and aresuccessively opened as the vehicle passes thereby, the entrance valveand the auxiliary valve being closed after a predetermined amount of airhas been admitted behind 5 the vehicle.

References Cited UNITED STATES PATENTS 3,438,337 4/1969 Edwards 104-138ARTHUR L. LA POINT, Primary Examiner D. W. KEEN, Assistant Examiner

